This document discusses using XHProf to perform performance tuning of PHP applications. It begins with an introduction of the speaker and their company Pardot. It then provides an overview of XHProf including how to install, configure, and use it to profile PHP applications. The document outlines various performance tips for PHP such as optimizing array operations, managing memory efficiently, and improving database queries. It also walks through some examples of profiling a sample Symfony application that involves getting click data from a database. The examples demonstrate how to optimize queries and object hydration to improve performance.

1. Performance Tuning with XHProf
Dan van Kley
Computerologist
Salesforce Pardot
dvankley@salesforce.com

3. Who I Am
PHP Convert
Recovering .NET developer
Backend Engineer
This isn’t a Javascript conference anyway
Lover of Automation
Automate all the things
Very Lazy and Slightly Paranoid
Not much of a web presence, just send me an email.

4. Who Pardot Is
ATL Represent!
We’re right by Lenox, come by and play some ping pong
B2B Marketing Automation Division of Salesforce
Odds are you don’t care about that part
Primary App in PHP
• ~600k authenticated requests/day
• ~20M API requests/day
• ~125M public endpoint requests/day
• ~175M background task executions/day
Recent PHP 7 Migration
It is great and you should use it
It’s not French

5. Why Performance Matters
User Experience
Page load times are critical to user satisfaction
Resource Efficiency
Do more with less, save $$$
Larger Workloads
Scale up without more hardware
Understand Your Stack
Know what your function calls are actually doing

6. Agenda
XHProf Basics
Performance Tips
Scenarios and Examples
Hopefully we can get to lunch early

7. XHProf Basics
Getting off the ground

8. What XHProf Is
PHP Extension
Written in C and linked into the runtime to provide low level instrumentation.
Hierarchical Profiler
Profile is a call hierarchy, not a strict “graph”. Callgraph does a better job of modeling.
Simple Frontend
Ships with a basic frontend, many other options available as well. Choose your own adventure!
Measurements per Function:
• Number of times called
• Inclusive/exclusive memory usage
• Inclusive/exclusive execution time

9. How to Install XHProf
Original Project Abandoned
Facebook runs HHVM now so they don’t care about
vanilla PHP profiling anymore
PHP 5.x
Original or Phacility’s fork
PHP 7.x
Older versions may work, if not consider Tideways
or longxinH forks
Installation
You will need to compile forks from source.
Homebrew/PECL has the old Facebook version.

10. How to Install XHProf
Configuration
• Include the XHProf extension in your php.ini
• Verify it loads with phpinfo() or php –i
• Configure xhprof.output_dir
Set up your Frontend
• Facebook’s original UI is simple and works well,
that’s what I’m using
• Original UI is a simple PHP app contained in
xhprof_html, just point your server at it
• There are tons of other frontend options

11. How to Run XHProf
Hard Coding
Add xhprof_enable() and xhprof_disable() to
specific code paths, this helps focus the profile.
Custom Triggered Script
Use auto_prepend_file config directive with some
sort of custom trigger
Read the Documentation
How you store the profile run results depends on
the frontend you chose and how you configured it

12. Where to Profile
Manual Performance Tests
Run your application through performance testing locally or in a staging environment
Automated Performance Tests
Next level. Set up automated tests on a fixed hardware platform and alert on performance regressions.
Do it Live!
Add a custom trigger script to a non-customer-facing production machine and profile real data

13. How to Read a Profile
Call Hierarchy
• Main display is a sortable list of all function calls
• Click on functions to drill down to their children
Fields
• Calls
• Wall time
• Memory usage
• Inclusive vs exclusive
Comparison
Vanilla UI has a feature to compare two different
runs

14. How to Read a Callgraph
Time Performance
Critical path graph can be helpful, but be careful
Percentage Time
Helps judge overall shape of execution path
Call Count Performance
Validate your assumptions
Big Red Box
Will often make your problem very obvious

15. Performance Tips

16. Array Operations
Use Arrays as Hash Sets
• Use array_flip() and isset()/array_key_exists() instead of in_array()
• array_intersect_key() instead of array_intersect()
• Use array union instead of array_merge()
Avoid Nested Iteration
Acceptable on bounded data sets, but be careful. Unbounded data sets will catch you by surprise.
Avoid Unnecessary Repetition
Don’t count() every iteration of a loop. It’s O(1) but it’s still not worth it.
Use Generators/Iterators
Avoid processing huge data sets at once. Process manageable chunks iteratively.

17. Managing Memory
Be Conservative
Don’t create objects or variables you don’t need. Obvious, I know.
Know Your Stack
Understand the basics of your libraries. They’re not magical black boxes.
Give Yourself Room
PHP’s default memory limit is pretty low. Don’t go nuts, but 128M is not enough for many workloads.
Copy-On-Write
Know how and why PHP copies array structs.

18. Managing Memory
Avoid Circular References
PHP’s garbage collector is not good with them. Sometimes they’re unavoidable, but be aware.
Avoid Long-Running Processes
PHP is built for short processes and tends to leak memory, so keep it short and fast.
gc_disable()
It worked for Composer!
Avoid Global/Class State
To keep active variable references to a minimum and because it’s a good idea in general

19. Database Queries (And Other External Calls)
Know Your ORM/DB Driver
It all boils down to SQL queries. Hydration is important, remember to clear the object graph regularly.
Know Your Database
You don’t have to be a DBA, but know the basics: indexes, transactions, prepared statements, easy/lazy
fetching of relations. Consider sorting/aggregation in PHP over the DB.
Batch Queries
Minimize network/transaction overhead by grouping queries in batches.
Caching
Can be complex, but is often very helpful. Have a healthy respect for it.

20. Other Stuff
Run PHP 7
No drawbacks and huge improvements
When in Doubt, Test
Profiling’s easy once you have it set up
Keep Digging
Don’t be afraid to look at the source
Try Other Tools
Other XHProf frontends, New Relic, Symfony
profiler, Blackfire, Xdebug profiler, etc.

21. Scenarios and Examples
Getting our hands dirty

22. Sample Application
Symfony 3 with Doctrine 2
Basic “link shortener” app, find it on Github
Schema
Users have many Links have many LinkClicks
Scale
50 users, 12k Links, 5M LinkClicks
Versions
MySQL 5.7, PHP 7.0

23. Get Clicks For Today In Order
Problem
Using the DB, get all clicks from today in order.
Assume the timestamp column is not and cannot be
indexed.
Straight Database Query
• Simplest solution
• SELECT * FROM link_click WHERE created_at >
DATE_SUB(CURDATE(), INTERVAL 1 DAY)
ORDER BY created_at DESC;
• Bad performance if not indexed
• What do we expect to see?

28. Get Clicks For Today In Order
Results
• Filesorts are pretty much always bad
• Alternatives?
Revised Query with PHP Aggregation
• Lose the ORDER BY
• Do sorting on the PHP side
Expectations
Roughly what do we expect to see?

32. Get Clicks For Today In Order
Results
• Much worse.
• Why?
• What can we do?
Change Hydration Method
• We expect sorting to take a while
• See a lot of time spent calling Doctrine accessors
and performing hydration
• Switch to scalar hydration

35. Get Clicks For Today In Order
Results
• Decent speedup
• Profile looks more as we expect
• Victory! (mostly)
Next Steps?
• DB index is still the best solution if possible
• Depending on when we do this operation,
consider caching or an alternate data store if we
can’t add an index
• Do we need to fetch the entire day at once?
Consider grabbing smaller time windows.

36. Get Clicks By User
Problem
Excluding DB interactions this time, given an array
of clicks, links, and user ids, group the clicks by user
id. Note that LinkClick does not have a direct
user_id reference. DB JOIN is the best solution, but
ignore that
Naïve Approach
For each link click, find the user id from the array of
links and shove the click into an associative array

39. Get Clicks By User
Result
• Terrible
• What’s the O(n) of this?
• What can we improve?
Avoid User Id Lookup
• One pass through Links to set up a mapping from
link_id to user_id to make lookups O(1)
• Should be much less terrible

43. Get Clicks By User
Result
• Much better
• Is this good enough?
• What else can we do?
Further Improvements
• Avoid in_array() call
• Avoid expensive ORM calls

44. Get Clicks By User
Result
• Not much better, but no drawbacks
• Would be more significant if there were a larger
number of user ids
• Doctrine 2’s scalar hydrator doesn’t include
foreign keys, would need more digging
• Victory?

45. Questions
And maybe answers, or maybe ignorance and snark

46. Thank Y u
Please review me on https://joind.in/talk/f45f2